The proposed research is designed to test a theoretical analysis of animal memory for asymmetric events on signal detection theory. Most animal memory procedures require a delayed discrimination between two events of roughly equal salience, but several seemingly unrelated lines of research have arranged memory tests for inherently unequal events. Examples include (a) memory for the presence vs. absence of an event, (b) memory for event duration (e.g., short vs. long), and memory for stimuli from different sensory modalities (e.g., tone vs. light). The proposed research tests a new theory of animal memory that attempts to provide a unified explanation for an interesting pattern of results common to each of these areas. That analysis may offer a general theory of memory for asymmetric events. The basic methodology used in most of the proposed experiments involves presenting one of two events that differ in salience, followed by a delay, followed by the presentation of two alternatives (red and green choice stimuli). A response to one color is reinforced with food on trials beginning with the less salient sample while a response to the other color is reinforced on trials beginning with the more salient sample. The discriminations to be tested include presence vs. absence, short vs. long duration, and tone vs. light. The signal detection analysis assumes that, in each case, the less salient stimulus is more like "nothing" than the more salient event. Several experiments are proposed to test this and related ideas. Additional experiments will investigate the mathematical form of the receiver operating characteristic (ROC) function. This approach has been used extensively in the human perception and human memory literatures to test the signal detection framework against competing accounts, and the same strategy is warranted here. The signal detection framework has been used to interpret findings from other studies on human recognition memory for more than two decades, but the use of this approach in the study of animal memory is comparatively rare. Identifying similarities and differences between animal and human memory is complicated by the absence of a coherent theoretical framework common to both species. Signal detection theory may offer one such framework, thereby facilitating the development of relevant animal models of memory impairment in humans.